1. Field of the Invention
The present invention relates to a color television receiver color correction circuit in which a vertical interval reference (VIR) signal is utilized to control a color level and/or hue.
2. Description of the Prior Art
In some prior art color television receivers, automatic adjustment of color saturation level or hue or both has been carried out by using a VIR signal which is part of the receiver signal. The VIR signal is an industry standard signal generated as part of a televison signal at a certain line interval during the vertical blanking interval. Although the VIR signal includes luminance and chrominance components that would be visible, they occur when the scanning beam of the picture tube is traversing a region that does not interfere with the picture being viewed.
The chrominance and luminance reference portions of the VIR signal have seen selected to correspond in amplitude to values that would be present during transmission of flesh tones of actors and actresses in the television picture. Viewers are aware of approximately what proper flesh tones should look like, while they may have no way of knowing the proper hue and saturation of other things in the picture.
U.S. Pat. No. 3,950,780 issued to Harry T. Freestone describes a prior art circuit for using a VIR signal to control hue and saturation. In that prior art circuit, the black reference level voltage is sampled and stored for comparison with a color reference signal. However, the color reference signal occurs at the beginning of each VIR signal line interval, and the black reference level voltage occurs at the end of the same line interval. As a result, the black reference level must be stored for almost a complete vertical interval. During that relatively long storage time the stored value may change, for example, due to leakage current, so that the comparison is inaccurate.